A 53-year-old West Roxbury man was identified Tuesday as the person who was killed in a single-vehicle crash on Morton Street near the Shea Rotary in Jamaica Plain, State Police said. Lawrence Mulhern was alone in his truck when it swerved off the road, rolled over, and hit a tree on Monday night, State Police said. Mulhern was pronounced dead at the scene. Mulhern worked in the MBTA’s power systems maintenance department and had worked for the agency since 1992, a spokeswoman said. The cause of the crash remains under investigation by State Police.